(NOT APPLICABLE)
(NOT APPLICABLE)
The present invention generally relates to lifting devices and, more particularly, to a pothole protection mechanism for a lift machine that helps to prevent a lift machine from tipping over when a pothole, bump, curb or other support threatening and tip generating hazard is encountered.
Typical pothole protection mechanisms contain horizontal bars or the like installed on sides of a vertical lift platform vehicle. The bars are deployed or extended when the platform is raised, and the bars are lifted or retracted when the platform is lowered to allow the machine to drive over ramps, obstacles and the like.
Current mechanisms have a mechanical link between the pothole protection mechanism and a lifting mechanism of the lifting platform. In a typical configuration, the lifting platform releases the pothole protection mechanism via a mechanical link or the like, and the pothole protection mechanism is deployed or extended by force of gravity and/or a system of springs. The deployment force is limited to avoid a crushing hazard to objects accidentally placed in the bar""s way. The limitation of the deployment force is done by mechanical means as only gravity and/or weak springs are used for deployment. A separate position sensor is used to verify full deployment of the mechanism. During lowering of the lifting platform, a component of the platform lifting mechanism, such as a scissors arm or a specially designed bracket attached to the scissors arm, pushes a mechanical linkage to raise the horizontal bars of the pothole protection mechanism.
An example of a related configuration is described in U.S. Pat. No. 5,890,737 to Hutka. A lifting device 10 includes a main frame 12 supported by a plurality of support members 14 such as wheels. A plurality of scissors members 16A-16F are arranged in a conventional criss-crossing manner to elevate and support a work platform 18. A hydraulic cylinder 20 raises and lowers the platform 18. A subframe 22 includes two large sheet metal boxes or trays that define a planar bottom wall 26. The mechanism includes structure for raising and lowering the subframe with respect to the ground due to movement of the platform 18.
It would be desirable in certain instances to extend or retract the pothole protection mechanism in a lift machine based on other factors than just position of the lifting platform. Such conditions may be related to (for example) load on the platform, position of the extendable deck, etc. On multipurpose machines, which can lift people and material using separate lifting devices, actuation can be initiated by load and position of the material handling device. Moreover, with the typical pothole protection mechanism construction, since there is a mechanical link between the lifting platform and the mechanism, the mechanical linkage must be sized to support the entire weight of the lifting platform. With known designs, the mechanical linkage can be divided into two subsystems: a linkage that supports the weight (which forms part of the new system) and a control (activation) linkage that provides a connection between the platform and the weight supporting linkagexe2x80x94this linkage, which is complicated and difficult to maintain, is eliminated in the proposed system. Using a small actuator to retract and possibly deploy the pothole protection mechanism could significantly reduce manufacturing and operational costs.
To obviate the problems associated with previous pothole protection mechanisms, a mechanism of the present invention is preferably raised and lowered by an independent actuator, i.e., without any mechanical linkage to the platform lifting component. Moreover, while lowering the pothole protection bar of the pothole protection mechanism, the actuator basically supports only the weight of the mechanism components, letting them descend in a controlled manner. When fully deployed, the support linkage for the pothole protection bar is positioned in an over-center position against a mechanical stop such that when the machine drops into a pothole or the like, its weight is supported by the bar and support linkage, and not by the actuator. As a consequence, the actuator can be sized for a force necessary only to lift the pothole protection mechanism, not to support the weight of the machine.
In accordance with an exemplary embodiment of the invention, a pothole protection mechanism for a lift machine includes a frame securable to the lift machine, a pothole protection bar movably coupled with the frame via a support linkage, and an actuator coupled between the frame and the pothole protection bar. As noted, the actuator is preferably sized for a force sufficient only to lift the pothole protection bar. As also noted, the pothole protection mechanism is preferably without a mechanical linkage for securing to a lifting component of the lift machine. The actuator may be an electromechanical actuator that drives the pothole protection bar between a retracted position and an extended position. Alternatively or additionally, the mechanism may include a latching assembly coupled between the frame and the pothole protection bar that releasably secures the pothole protection bar in the retracted position. In this context, the actuator drives the pothole protection bar from the extended position to the retracted position.
The support linkage may include a pair of two-link joints that pivot at a link attachment point with each of the two-link joints being secured at a first end to opposite sides of the frame, respectively, and at a second end to the pothole protection bar. A coupling bar is attached to each link attachment point of the two-link joints between the two-link joints, and the actuator is attached to the coupling bar. In this context, the pothole protection bar is movable between a retracted position and an extended position, and in the extended position, the two-link joints are pivoted to an over-center position and the coupling bar is abutted against a stop. In a preferred configuration, the actuator is in an extended position when the pothole protection bar is in its retracted position, and the actuator is in a retracted position when the pothole protection bar is in its extended position.
In an alternative arrangement, the support linkage includes a coupling bar driven by the actuator that pivots a joint secured between the frame and the pothole protection bar between an extended position and a retracted position. The coupling bar is abutted against a stop when the joint is in the extended position.
The actuator may include stroke switches that provide a signal to indicate when the pothole protection bar is in a fully extended position and a fully retracted position, respectively. Moreover, the actuator may include structure for detecting obstacles in a path of the pothole protection bar, such as a current-monitoring circuit coupled with the actuator that monitors current to the actuator.
In accordance with another exemplary embodiment of the invention, a lift machine includes a base supporting a lifting platform, the lifting platform being displaceable between a lowered position and a raised position via a lifting mechanism, and the pothole protection mechanism of the present invention. With the lift machine of the invention, the frame of the pothole protection mechanism is secured to the base. Wheels may be rotatably mounted on respective axles secured to the base, and a driving system coupled with the wheels provides motive power to the wheels.
A sensor monitors a position of the lifting platform. In this context, the pothole protection mechanism may further include a controller communicating with the sensor, the driving system and the actuator. The controller controls operation of the driving system and the actuator based on a signal received from the sensor. The controller is configured such that when the lifting platform is raised above the lowered position beyond a trigger point, the controller prevents operation of the driving system until the pothole protection mechanism is fully deployed. Additionally, when the lifting platform is raised above the lowered position beyond a trigger point and the pothole protection mechanism is deployed, the controller prevents retraction of the pothole protection mechanism until the lifting platform is lowered below the trigger point. The actuator preferably includes structure for detecting obstacles in a path of the pothole protection bar, wherein the controller prevents operation of the driving mechanism and operation of the pothole protection mechanism if an obstacle is detected in the path of the pothole protection bar.
The controller generally controls operation of the pothole protection mechanism according to factors independent of the lifting platform height. If the lift machine includes a platform extension coupled with the lifting platform, one of the factors for controlling operation of the pothole protection mechanism may include a position of the platform extension. Additionally, other factors for controlling operation of the pothole protection mechanism include any of a position of a material handling device, a load on the platform, a load on the material handling device, a configuration of the lift machine, etc.